2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * Code to connect to a remote host, and to perform the client side of the
6 * login (authentication) dialog.
8 * As far as I am concerned, the code I have written for this software
9 * can be used freely for any purpose. Any derived versions of this
10 * software must be clearly marked as such, and if the derived work is
11 * incompatible with the protocol description in the RFC file, it must be
12 * called by a name other than "ssh" or "Secure Shell".
16 RCSID("$OpenBSD: sshconnect.c,v 1.119 2002/01/21 15:13:51 markus Exp $");
18 #include <openssl/bn.h>
28 #include "sshconnect.h"
36 char *client_version_string = NULL;
37 char *server_version_string = NULL;
39 extern Options options;
40 extern char *__progname;
42 #ifndef INET6_ADDRSTRLEN /* for non IPv6 machines */
43 #define INET6_ADDRSTRLEN 46
47 sockaddr_ntop(struct sockaddr *sa)
50 static char addrbuf[INET6_ADDRSTRLEN];
52 switch (sa->sa_family) {
54 addr = &((struct sockaddr_in *)sa)->sin_addr;
57 addr = &((struct sockaddr_in6 *)sa)->sin6_addr;
60 /* This case should be protected against elsewhere */
61 abort(); /* XXX abort is bad -- do something else */
63 inet_ntop(sa->sa_family, addr, addrbuf, sizeof(addrbuf));
68 * Connect to the given ssh server using a proxy command.
71 ssh_proxy_connect(const char *host, u_short port, struct passwd *pw,
72 const char *proxy_command)
79 char strport[NI_MAXSERV];
81 /* Convert the port number into a string. */
82 snprintf(strport, sizeof strport, "%hu", port);
84 /* Build the final command string in the buffer by making the
85 appropriate substitutions to the given proxy command. */
86 buffer_init(&command);
87 for (cp = proxy_command; *cp; cp++) {
88 if (cp[0] == '%' && cp[1] == '%') {
89 buffer_append(&command, "%", 1);
93 if (cp[0] == '%' && cp[1] == 'h') {
94 buffer_append(&command, host, strlen(host));
98 if (cp[0] == '%' && cp[1] == 'p') {
99 buffer_append(&command, strport, strlen(strport));
103 buffer_append(&command, cp, 1);
105 buffer_append(&command, "\0", 1);
107 /* Get the final command string. */
108 command_string = buffer_ptr(&command);
110 /* Create pipes for communicating with the proxy. */
111 if (pipe(pin) < 0 || pipe(pout) < 0)
112 fatal("Could not create pipes to communicate with the proxy: %.100s",
115 debug("Executing proxy command: %.500s", command_string);
117 /* Fork and execute the proxy command. */
118 if ((pid = fork()) == 0) {
121 /* Child. Permanently give up superuser privileges. */
122 permanently_set_uid(pw);
124 /* Redirect stdin and stdout. */
127 if (dup2(pin[0], 0) < 0)
128 perror("dup2 stdin");
132 if (dup2(pout[1], 1) < 0)
133 perror("dup2 stdout");
134 /* Cannot be 1 because pin allocated two descriptors. */
137 /* Stderr is left as it is so that error messages get
138 printed on the user's terminal. */
139 argv[0] = _PATH_BSHELL;
141 argv[2] = command_string;
144 /* Execute the proxy command. Note that we gave up any
145 extra privileges above. */
146 execv(argv[0], argv);
152 fatal("fork failed: %.100s", strerror(errno));
154 /* Close child side of the descriptors. */
158 /* Free the command name. */
159 buffer_free(&command);
161 /* Set the connection file descriptors. */
162 packet_set_connection(pout[0], pin[1]);
164 /* Indicate OK return */
169 * Creates a (possibly privileged) socket for use as the ssh connection.
172 ssh_create_socket(struct passwd *pw, int privileged, int family)
175 struct addrinfo hints, *res;
178 * If we are running as root and want to connect to a privileged
179 * port, bind our own socket to a privileged port.
182 int p = IPPORT_RESERVED - 1;
183 sock = rresvport_af(&p, family);
185 error("rresvport: af=%d %.100s", family, strerror(errno));
187 debug("Allocated local port %d.", p);
191 * Just create an ordinary socket on arbitrary port. We use
192 * the user's uid to create the socket.
194 temporarily_use_uid(pw);
195 sock = socket(family, SOCK_STREAM, 0);
197 error("socket: %.100s", strerror(errno));
200 /* Bind the socket to an alternative local IP address */
201 if (options.bind_address == NULL)
204 memset(&hints, 0, sizeof(hints));
205 hints.ai_family = family;
206 hints.ai_socktype = SOCK_STREAM;
207 hints.ai_flags = AI_PASSIVE;
208 gaierr = getaddrinfo(options.bind_address, "0", &hints, &res);
210 error("getaddrinfo: %s: %s", options.bind_address,
211 gai_strerror(gaierr));
215 if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
216 error("bind: %s: %s", options.bind_address, strerror(errno));
226 * Opens a TCP/IP connection to the remote server on the given host.
227 * The address of the remote host will be returned in hostaddr.
228 * If port is 0, the default port will be used. If anonymous is zero,
229 * a privileged port will be allocated to make the connection.
230 * This requires super-user privileges if anonymous is false.
231 * Connection_attempts specifies the maximum number of tries (one per
232 * second). If proxy_command is non-NULL, it specifies the command (with %h
233 * and %p substituted for host and port, respectively) to use to contact
237 * ECONNREFUSED if we got a "Connection Refused" by the peer on any address
238 * ECONNABORTED if we failed without a "Connection refused"
239 * Suitable error messages for the connection failure will already have been
243 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
244 u_short port, int family, int connection_attempts,
245 int anonymous, struct passwd *pw, const char *proxy_command)
249 int sock = -1, attempt;
250 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
251 struct addrinfo hints, *ai, *aitop;
252 struct linger linger;
255 * Did we get only other errors than "Connection refused" (which
256 * should block fallback to rsh and similar), or did we get at least
257 * one "Connection refused"?
259 int full_failure = 1;
261 debug("ssh_connect: getuid %u geteuid %u anon %d",
262 (u_int) getuid(), (u_int) geteuid(), anonymous);
264 /* Get default port if port has not been set. */
266 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
268 port = ntohs(sp->s_port);
270 port = SSH_DEFAULT_PORT;
272 /* If a proxy command is given, connect using it. */
273 if (proxy_command != NULL)
274 return ssh_proxy_connect(host, port, pw, proxy_command);
276 /* No proxy command. */
278 memset(&hints, 0, sizeof(hints));
279 hints.ai_family = family;
280 hints.ai_socktype = SOCK_STREAM;
281 snprintf(strport, sizeof strport, "%d", port);
282 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
283 fatal("%s: %.100s: %s", __progname, host,
284 gai_strerror(gaierr));
287 * Try to connect several times. On some machines, the first time
288 * will sometimes fail. In general socket code appears to behave
289 * quite magically on many machines.
291 for (attempt = 0; ;) {
293 debug("Trying again...");
295 /* Loop through addresses for this host, and try each one in
296 sequence until the connection succeeds. */
297 for (ai = aitop; ai; ai = ai->ai_next) {
298 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
300 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
301 ntop, sizeof(ntop), strport, sizeof(strport),
302 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
303 error("ssh_connect: getnameinfo failed");
306 debug("Connecting to %.200s [%.100s] port %s.",
307 host, ntop, strport);
309 /* Create a socket for connecting. */
310 sock = ssh_create_socket(pw,
314 !anonymous && geteuid() == 0,
318 /* Any error is already output */
321 /* Connect to the host. We use the user's uid in the
322 * hope that it will help with tcp_wrappers showing
323 * the remote uid as root.
325 temporarily_use_uid(pw);
326 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
327 /* Successful connection. */
328 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
332 if (errno == ECONNREFUSED)
334 log("ssh: connect to address %s port %s: %s",
335 sockaddr_ntop(ai->ai_addr), strport,
339 * Close the failed socket; there appear to
340 * be some problems when reusing a socket for
341 * which connect() has already returned an
348 break; /* Successful connection. */
351 if (attempt >= connection_attempts)
353 /* Sleep a moment before retrying. */
359 /* Return failure if we didn't get a successful connection. */
360 if (attempt >= connection_attempts)
361 return full_failure ? ECONNABORTED : ECONNREFUSED;
363 debug("Connection established.");
366 * Set socket options. We would like the socket to disappear as soon
367 * as it has been closed for whatever reason.
369 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
372 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
374 /* Set keepalives if requested. */
375 if (options.keepalives &&
376 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
378 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
380 /* Set the connection. */
381 packet_set_connection(sock, sock);
387 * Waits for the server identification string, and sends our own
388 * identification string.
391 ssh_exchange_identification(void)
393 char buf[256], remote_version[256]; /* must be same size! */
394 int remote_major, remote_minor, i, mismatch;
395 int connection_in = packet_get_connection_in();
396 int connection_out = packet_get_connection_out();
397 int minor1 = PROTOCOL_MINOR_1;
399 /* Read other side\'s version identification. */
401 for (i = 0; i < sizeof(buf) - 1; i++) {
402 int len = atomicio(read, connection_in, &buf[i], 1);
404 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
406 fatal("ssh_exchange_identification: Connection closed by remote host");
407 if (buf[i] == '\r') {
410 continue; /**XXX wait for \n */
412 if (buf[i] == '\n') {
417 buf[sizeof(buf) - 1] = 0;
418 if (strncmp(buf, "SSH-", 4) == 0)
420 debug("ssh_exchange_identification: %s", buf);
422 server_version_string = xstrdup(buf);
425 * Check that the versions match. In future this might accept
426 * several versions and set appropriate flags to handle them.
428 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
429 &remote_major, &remote_minor, remote_version) != 3)
430 fatal("Bad remote protocol version identification: '%.100s'", buf);
431 debug("Remote protocol version %d.%d, remote software version %.100s",
432 remote_major, remote_minor, remote_version);
434 compat_datafellows(remote_version);
437 switch (remote_major) {
439 if (remote_minor == 99 &&
440 (options.protocol & SSH_PROTO_2) &&
441 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
445 if (!(options.protocol & SSH_PROTO_1)) {
449 if (remote_minor < 3) {
450 fatal("Remote machine has too old SSH software version.");
451 } else if (remote_minor == 3 || remote_minor == 4) {
452 /* We speak 1.3, too. */
455 if (options.forward_agent) {
456 log("Agent forwarding disabled for protocol 1.3");
457 options.forward_agent = 0;
462 if (options.protocol & SSH_PROTO_2) {
472 fatal("Protocol major versions differ: %d vs. %d",
473 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
475 /* Send our own protocol version identification. */
476 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
477 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
478 compat20 ? PROTOCOL_MINOR_2 : minor1,
480 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
481 fatal("write: %.100s", strerror(errno));
482 client_version_string = xstrdup(buf);
483 chop(client_version_string);
484 chop(server_version_string);
485 debug("Local version string %.100s", client_version_string);
488 /* defaults to 'no' */
490 confirm(const char *prompt)
492 const char *msg, *again = "Please type 'yes' or 'no': ";
496 if (options.batch_mode)
498 for (msg = prompt;;msg = again) {
499 p = read_passphrase(msg, RP_ECHO);
501 (p[0] == '\0') || (p[0] == '\n') ||
502 strncasecmp(p, "no", 2) == 0)
504 if (strncasecmp(p, "yes", 3) == 0)
514 * check whether the supplied host key is valid, return -1 if the key
515 * is not valid. the user_hostfile will not be updated if 'readonly' is true.
519 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
520 int readonly, const char *user_hostfile, const char *system_hostfile)
523 char *type = key_type(host_key);
525 char hostline[1000], *hostp, *fp;
526 HostStatus host_status;
527 HostStatus ip_status;
528 int local = 0, host_ip_differ = 0;
530 char ntop[NI_MAXHOST];
532 int len, host_line, ip_line;
533 const char *host_file = NULL, *ip_file = NULL;
536 * Force accepting of the host key for loopback/localhost. The
537 * problem is that if the home directory is NFS-mounted to multiple
538 * machines, localhost will refer to a different machine in each of
539 * them, and the user will get bogus HOST_CHANGED warnings. This
540 * essentially disables host authentication for localhost; however,
541 * this is probably not a real problem.
543 /** hostaddr == 0! */
544 switch (hostaddr->sa_family) {
546 local = (ntohl(((struct sockaddr_in *)hostaddr)->
547 sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
548 salen = sizeof(struct sockaddr_in);
551 local = IN6_IS_ADDR_LOOPBACK(
552 &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
553 salen = sizeof(struct sockaddr_in6);
557 salen = sizeof(struct sockaddr_storage);
560 if (options.no_host_authentication_for_localhost == 1 && local &&
561 options.host_key_alias == NULL) {
562 debug("Forcing accepting of host key for "
563 "loopback/localhost.");
568 * We don't have the remote ip-address for connections
569 * using a proxy command
571 if (options.proxy_command == NULL) {
572 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
573 NULL, 0, NI_NUMERICHOST) != 0)
574 fatal("check_host_key: getnameinfo failed");
577 ip = xstrdup("<no hostip for proxy command>");
580 * Turn off check_host_ip if the connection is to localhost, via proxy
581 * command or if we don't have a hostname to compare with
583 if (options.check_host_ip &&
584 (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
585 options.check_host_ip = 0;
588 * Allow the user to record the key under a different name. This is
589 * useful for ssh tunneling over forwarded connections or if you run
590 * multiple sshd's on different ports on the same machine.
592 if (options.host_key_alias != NULL) {
593 host = options.host_key_alias;
594 debug("using hostkeyalias: %s", host);
598 * Store the host key from the known host file in here so that we can
599 * compare it with the key for the IP address.
601 file_key = key_new(host_key->type);
604 * Check if the host key is present in the user\'s list of known
605 * hosts or in the systemwide list.
607 host_file = user_hostfile;
608 host_status = check_host_in_hostfile(host_file, host, host_key,
609 file_key, &host_line);
610 if (host_status == HOST_NEW) {
611 host_file = system_hostfile;
612 host_status = check_host_in_hostfile(host_file, host, host_key,
613 file_key, &host_line);
616 * Also perform check for the ip address, skip the check if we are
617 * localhost or the hostname was an ip address to begin with
619 if (options.check_host_ip) {
620 Key *ip_key = key_new(host_key->type);
622 ip_file = user_hostfile;
623 ip_status = check_host_in_hostfile(ip_file, ip, host_key,
625 if (ip_status == HOST_NEW) {
626 ip_file = system_hostfile;
627 ip_status = check_host_in_hostfile(ip_file, ip,
628 host_key, ip_key, &ip_line);
630 if (host_status == HOST_CHANGED &&
631 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
636 ip_status = host_status;
640 switch (host_status) {
642 /* The host is known and the key matches. */
643 debug("Host '%.200s' is known and matches the %s host key.",
645 debug("Found key in %s:%d", host_file, host_line);
646 if (options.check_host_ip && ip_status == HOST_NEW) {
648 log("%s host key for IP address "
649 "'%.128s' not in list of known hosts.",
651 else if (!add_host_to_hostfile(user_hostfile, ip,
653 log("Failed to add the %s host key for IP "
654 "address '%.128s' to the list of known "
655 "hosts (%.30s).", type, ip, user_hostfile);
657 log("Warning: Permanently added the %s host "
658 "key for IP address '%.128s' to the list "
659 "of known hosts.", type, ip);
665 /* The host is new. */
666 if (options.strict_host_key_checking == 1) {
668 * User has requested strict host key checking. We
669 * will not add the host key automatically. The only
670 * alternative left is to abort.
672 error("No %s host key is known for %.200s and you "
673 "have requested strict checking.", type, host);
675 } else if (options.strict_host_key_checking == 2) {
677 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
678 snprintf(msg, sizeof(msg),
679 "The authenticity of host '%.200s (%s)' can't be "
681 "%s key fingerprint is %s.\n"
682 "Are you sure you want to continue connecting "
683 "(yes/no)? ", host, ip, type, fp);
688 if (options.check_host_ip && ip_status == HOST_NEW) {
689 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
695 * If not in strict mode, add the key automatically to the
696 * local known_hosts file.
698 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
699 log("Failed to add the host to the list of known "
700 "hosts (%.500s).", user_hostfile);
702 log("Warning: Permanently added '%.200s' (%s) to the "
703 "list of known hosts.", hostp, type);
706 if (options.check_host_ip && host_ip_differ) {
708 if (ip_status == HOST_NEW)
710 else if (ip_status == HOST_OK)
711 msg = "is unchanged";
713 msg = "has a different value";
714 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
715 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
716 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
717 error("The %s host key for %s has changed,", type, host);
718 error("and the key for the according IP address %s", ip);
719 error("%s. This could either mean that", msg);
720 error("DNS SPOOFING is happening or the IP address for the host");
721 error("and its host key have changed at the same time.");
722 if (ip_status != HOST_NEW)
723 error("Offending key for IP in %s:%d", ip_file, ip_line);
725 /* The host key has changed. */
726 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
727 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
728 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
729 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
730 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
731 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
732 error("It is also possible that the %s host key has just been changed.", type);
733 error("The fingerprint for the %s key sent by the remote host is\n%s.",
735 error("Please contact your system administrator.");
736 error("Add correct host key in %.100s to get rid of this message.",
738 error("Offending key in %s:%d", host_file, host_line);
742 * If strict host key checking is in use, the user will have
743 * to edit the key manually and we can only abort.
745 if (options.strict_host_key_checking) {
746 error("%s host key for %.200s has changed and you have "
747 "requested strict checking.", type, host);
752 * If strict host key checking has not been requested, allow
753 * the connection but without password authentication or
756 if (options.password_authentication) {
757 error("Password authentication is disabled to avoid "
758 "man-in-the-middle attacks.");
759 options.password_authentication = 0;
761 if (options.forward_agent) {
762 error("Agent forwarding is disabled to avoid "
763 "man-in-the-middle attacks.");
764 options.forward_agent = 0;
766 if (options.forward_x11) {
767 error("X11 forwarding is disabled to avoid "
768 "man-in-the-middle attacks.");
769 options.forward_x11 = 0;
771 if (options.num_local_forwards > 0 ||
772 options.num_remote_forwards > 0) {
773 error("Port forwarding is disabled to avoid "
774 "man-in-the-middle attacks.");
775 options.num_local_forwards =
776 options.num_remote_forwards = 0;
779 * XXX Should permit the user to change to use the new id.
780 * This could be done by converting the host key to an
781 * identifying sentence, tell that the host identifies itself
782 * by that sentence, and ask the user if he/she whishes to
783 * accept the authentication.
788 if (options.check_host_ip && host_status != HOST_CHANGED &&
789 ip_status == HOST_CHANGED) {
790 snprintf(msg, sizeof(msg),
791 "Warning: the %s host key for '%.200s' "
792 "differs from the key for the IP address '%.128s'"
793 "\nOffending key for IP in %s:%d",
794 type, host, ip, ip_file, ip_line);
795 if (host_status == HOST_OK) {
797 snprintf(msg + len, sizeof(msg) - len,
798 "\nMatching host key in %s:%d",
799 host_file, host_line);
801 if (options.strict_host_key_checking == 1) {
803 error("Exiting, you have requested strict checking.");
805 } else if (options.strict_host_key_checking == 2) {
806 strlcat(msg, "\nAre you sure you want "
807 "to continue connecting (yes/no)? ", sizeof(msg));
824 verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
828 /* return ok if the key can be found in an old keyfile */
829 if (stat(options.system_hostfile2, &st) == 0 ||
830 stat(options.user_hostfile2, &st) == 0) {
831 if (check_host_key(host, hostaddr, host_key, /*readonly*/ 1,
832 options.user_hostfile2, options.system_hostfile2) == 0)
835 return check_host_key(host, hostaddr, host_key, /*readonly*/ 0,
836 options.user_hostfile, options.system_hostfile);
840 * Starts a dialog with the server, and authenticates the current user on the
841 * server. This does not need any extra privileges. The basic connection
842 * to the server must already have been established before this is called.
843 * If login fails, this function prints an error and never returns.
844 * This function does not require super-user privileges.
847 ssh_login(Key **keys, int nkeys, const char *orighost,
848 struct sockaddr *hostaddr, struct passwd *pw)
851 char *server_user, *local_user;
853 local_user = xstrdup(pw->pw_name);
854 server_user = options.user ? options.user : local_user;
856 /* Convert the user-supplied hostname into all lowercase. */
857 host = xstrdup(orighost);
858 for (cp = host; *cp; cp++)
862 /* Exchange protocol version identification strings with the server. */
863 ssh_exchange_identification();
865 /* Put the connection into non-blocking mode. */
866 packet_set_nonblocking();
869 /* authenticate user */
871 ssh_kex2(host, hostaddr);
872 ssh_userauth2(local_user, server_user, host, keys, nkeys);
874 ssh_kex(host, hostaddr);
875 ssh_userauth1(local_user, server_user, host, keys, nkeys);
880 ssh_put_password(char *password)
885 if (datafellows & SSH_BUG_PASSWORDPAD) {
886 packet_put_cstring(password);
889 size = roundup(strlen(password) + 1, 32);
890 padded = xmalloc(size);
891 memset(padded, 0, size);
892 strlcpy(padded, password, size);
893 packet_put_string(padded, size);
894 memset(padded, 0, size);